Polarization recovery system using redirection

ABSTRACT

A polarization recovery system includes a polarizing beam splitter transmitting light of a useful polarization in an output direction and reflecting light of a non-useful polarization in a first orthogonal direction substantially orthogonal to the output direction. An initial reflector may reflect the non-useful polarization light in a second orthogonal direction substantially orthogonal to the output direction and the first orthogonal direction, and a final reflector may reflect the non-useful polarization light in the output direction. The non-useful polarization light may be rotated substantially to light of the useful polarization by the initial and final reflectors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 10/781,940 filed Feb. 20, 2004, which claims priority to ProvisionalApplication Ser. Nos. 60/448,471, filed Feb. 21, 2003, and 60/469,393,filed May 12, 2003, and which is a continuation-in-part of applicationSer. No. 10/347,522, filed Jan. 21, 2003, which is a continuation ofapplication Ser. No. 09/814,970, filed Mar. 23, 2001, now U.S. Pat. No.6,587,269. Each of which are incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to the recovery of light that might otherwise beunused in projection systems.

2. Description of the Related Art

Projection displays work by projecting light onto a screen. The light isarranged in patterns of colors or brightness and darkness or both. Thepatterns are viewed by a viewer who assimilates them by associating thepatterns with images with which the viewer may already be familiar, suchas characters or faces. The patterns may be formed in various ways. Oneway to form patterns is by modulating a beam of light with a stream ofinformation.

Polarized light may be modulated by filtering it with polarized filters.Polarized filters will pass light, in general, if their polarizationmatches the polarization of the incident light. A liquid crystal display(LCD) imager may be used to perform the modulation in LCD-typeprojection displays. The LCD imager may include pixels that may bemodulated by altering their polarization to either match or differ fromthe polarization of incident light. The light input to the LCD imager ispolarized such that when the LCD pixels are modulated the polarizationof the selected pixels is changed, and when the light output from theimager is analyzed by another polarizer, the selected pixels will bedarkened. The pattern may be projected onto a screen as the presence orabsence of light. If the polarization of the pixels is modulated withinformation in a pattern with which a viewer is familiar, the viewer mayrecognize the pattern projected onto the screen.

One way to polarize light for an LCD imager is with a polarizing beamsplitter (PBS). Polarized light may be provided to an imaging systemwith an array of lenses, such as a fly's eye lens, and an array ofpolarizing beam splitters. A parabolic reflector may be used with afly's-eye lens to focus light such that the light is nearly parallel.The beam is split into many sections by the lens array and each sectionis refocused by another lens array into the polarizing beam splitterarray. A parabolic reflector, however, may reduce the brightness of asource of light, such as an arc. Furthermore, the efficiency of afly's-eye lens recovery system depends critically on the alignment ofthe two lens arrays and the polarizing beam splitter array. Finally, apolarization recovery system comprised of a parabolic reflector and afly's-eye lens may not be suited for sequential color single imagersystems.

Elliptical reflectors may be used with a light pipe and a color wheel toproduce sequential colors as well. Such a system, however, stillrequires a polarization recovery system and does not solve the intrinsicloss of brightness associated with ellipsoidal reflectors. The lightoutput from the polarizing beam splitter array will then be linearlypolarized and focused into the target. Each polarizing beam splitterdivides unpolarized light into beams having disparate polarizations.Only one of the beams will be of the correct polarization to input tothe LCD imager after the light is polarized. The other beam will be ofan incorrect polarization and hence unusable directly.

Polarization recovery systems may be used to recover light of the unusedpolarization by converting it into usable light with the correctpolarization. Various schemes have been developed to convert theincorrectly polarized light to the correct polarization so that it toomay be used. One method, shown in FIG. 1, is to transmit light of afirst polarization 102 from a polarizing beam splitter 104 directly toan output 106 while reflecting light of a second polarization 108 at anangle to the output 106, such as a 90° angle. The light of the secondpolarization 108 is then reflected so it is parallel the light of thefirst polarization 102, heading toward the output 106. A retarder plate110, e.g. a quarter wave or half wave plate, is placed in the path ofthe light of the second polarization 108 to rotate it into light of thefirst polarization 102 such the output consists of light of only thefirst polarization 102.

Retarder plates rotate light from one polarization to another by slowinglight in one plane down while allowing light in the opposite plane topass relatively unimpeded. The speed at which light propagates through amedium is, in general, related to its wavelength. The degree to whichlight is slowed down will thus also be related to its wavelength. Sinceretarder plates that are applied to broadband light must pass light of arange of wavelengths, some light will be retarded more than other light.Retarder plates are, in general, tuned to a particular wavelength. Inparticular, wavelengths that are longer or shorter than the tunedwavelength will not be completely rotated from the unusable polarizationto the correct polarization. Thus some of the light of wavelengthslonger or shorter than the tuned wavelength will be lost, or at leastnot recovered. Retarder plates, furthermore, are relatively expensiveand often not reliable. A retarder plate makes a polarization recoverysystem itself expensive and unreliable.

Although these systems have been used commercially, the cost of thecomponents is high and they require critical alignments and opticaldesigns. As a result, there is a need for a system to performpolarization conversion with high efficiency, simple configurations andlower costs.

SUMMARY OF THE INVENTION

In a first aspect of the invention a polarization recovery system mayinclude a polarizing beam splitter transmitting a light of a usefulpolarization in an output direction and reflecting a light of anon-useful polarization in a first orthogonal direction substantiallyorthogonal to the output direction, an initial reflector disposedreflectably to the first orthogonal direction, the initial reflectorreflecting the non-useful polarization light in a second orthogonaldirection substantially orthogonal to the output direction and the firstorthogonal direction, and a final reflector disposed reflectably to thesecond orthogonal direction, the final reflector reflecting thenon-useful polarization light in the output direction, wherein thenon-useful polarization light is rotated substantially to light of theuseful polarization by the initial and final reflectors.

In a second aspect of the invention a method of polarization recoverymay include polarizing substantially light into light of a usefulpolarization and light of a non-useful polarization, transmitting theuseful polarization light in an output direction, reflecting thenon-useful polarization light in a first orthogonal directionsubstantially orthogonal to the output direction, reflecting thenon-useful polarization light in a second orthogonal directionsubstantially orthogonal to the output direction and the firstorthogonal direction, and reflecting the non-useful polarization lightin the output direction.

In a third aspect of the invention a system of polarization recovery mayinclude means for polarizing substantially light into light of a usefulpolarization and light of a non-useful polarization, means fortransmitting the useful light in an output direction, means forreflecting the non-useful light in a first orthogonal directionsubstantially orthogonal to the output direction, means for reflectingthe non-useful light in a second orthogonal direction substantiallyorthogonal to the output direction and the first orthogonal direction,and means for reflecting the non-useful light in the output direction.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a polarization recovery system;

FIG. 2 shows a schematic diagram of a polarization recovery systemaccording to an embodiment of the invention;

FIGS. 3 and 3B show a polarization recovery apparatus for use with anembodiment of the invention;

FIGS. 4 and 4B show a polarization recovery apparatus for use with anembodiment of the invention;

FIG. 5 shows a polarization recovery apparatus for use with anembodiment of the invention;

FIGS. 6A-6C show straight and tapered light pipes for use with anembodiment of the invention;

FIGS. 7A-7H show various cross-sections of light pipes for use with anembodiment of the invention;

FIGS. 8A-8E show various configurations of light pipes for use with anembodiment of the invention;

FIG. 9 shows a polarization recovery apparatus for use with anembodiment of the invention; and

FIGS. 10 A-C show various input and output surfaces of light pipes foruse with an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It would be desirable if light of an unusable polarization could berecovered and used by converting its polarization to a correct, oruseful, polarization. Since a retarder plate makes a polarizationrecovery system more expensive and less reliable, it would be desirablefor polarization recovery to be performed without resorting to the useof retarder plates. It would be desirable for polarization recovery tobe performed on broadband radiation. It would be desirable for apolarization recovery system to be relatively simple to manufacture andassemble. It would be desirable for a polarization recovery system toallow the use of a color wheel in a single imager system.

In FIG. 2 is shown a polarization recovery system 200 according to afirst embodiment of the invention. Polarization recovery system 200 mayinclude a polarizing beam splitter 202, such as a multi-layer coated ora wire-grid polarizing beam splitter. In one embodiment, light input topolarizing beam splitter 202 may come directly or indirectly from asource 212 of electromagnetic radiation, i.e. light. In one embodiment,source 212 of electro-magnetic radiation may be an arc lamp, such as axenon lamp, a metal halide lamp, a high intensity discharge (HID) lamp,or a mercury lamp. In another embodiment, source 212 may be a halogenlamp or a filament lamp.

In one embodiment, polarization recovery system 200 may include an inputlight pipe 224, a supercube 268, and an output light pipe 232, as shownin FIGS. 2 and 5. In several embodiments, output light pipe 232 may bean homogenizer or an integrator. The output of input light pipe 224 maybe coupled into the prism arrangement, i.e. supercube 268. Input lightpipe 224 may use total internal reflection (TIR) to propagate light tosupercube 268.

In several embodiments, input light pipe 224, output light pipe 232, orboth input light and output light pipes 224 and 232 may be increasingtaper light pipes, as shown in FIG. 6A, decreasing taper light pipes, asshown in FIG. 6B, or straight light pipes, as shown in FIG. 6C. Inseveral embodiments, a cross-section of input light pipe 224, outputlight pipe 232, or both input light and output light pipes 224 and 232may be rectangular, circular, triangular, rhomboid, trapezoidal,pentagonal, hexagonal, or octagonal, as shown in FIGS. 7A-7H. In severalembodiments, input light pipe 224, output light pipe 232, or both inputlight and output light pipes 224 and 232 may be comprised of an opticalfiber, an optical fiber bundle, a fused fiber bundle, a polygonalwaveguide, or a hollow light pipe, as shown in FIGS. 8A-8E.

Several embodiments of polarization recovery system 200 are shown inFIGS. 3 and 4. Polarizing beam splitter 202 may separate unpolarizedlight from input light pipe 224 into light of a useful polarization 204having a polarization 270, as shown in FIGS. 3A and 4A, and light ofnon-useful polarization 208 having a polarization 272, as shown in FIGS.3B and 4B. Polarizing beam splitter 202 may transmit light of usefulpolarization 204 in an output direction 206 and reflect light ofnon-useful polarization 208 in a first orthogonal direction 210substantially orthogonal to output direction 206. In one embodiment,polarization 270 may be substantially p-polarized, or horizontallypolarized, light, while polarization 272 is substantially s-polarized,or vertically polarized, light. In an alternative embodiment, the planesof polarization may be reversed.

Light of useful polarization 204 may propagate through polarizing beamsplitter 202 and be redirected by first output reflector 220 and secondoutput reflector 222, exiting second output reflector 222 withpolarization 270 unchanged, as shown in FIGS. 3A and 4A. Light ofnon-useful polarization 208, on the other hand, may be reflected by aninitial reflector 214 after exiting polarizing beam splitter 202, asshown in FIGS. 3B and 4B. Initial reflector 214 may reflect light ofnon-useful polarization 208 about an axis substantially orthogonal tothe plane of polarization 272 of light of non-useful polarization 208,which is in this case the s or vertical plane. Final reflector 218 maythen reflect light of non-useful polarization 208 in a directionparallel to output direction 206. An inclined surface of initialreflector 214 may thus be rotated 90° with respect to final reflector218. Although light of non-useful polarization 208 is still labeledlight of non-useful polarization 208 for tracking purposes, it hasbecome light of useful polarization, since the plane of polarization oflight of non-useful polarization 208 is now horizontal, or p-polarized,to substantially match that of light of useful polarization 204. In oneembodiment, both light of useful polarization 204 and light ofnon-useful polarization 208 may be coupled to output light pipe 232 andhomogenized.

In one embodiment, a first output reflector 220 may be disposedreflectably to output direction 206. First output reflector 220 mayreflect useful polarization light 204 in second orthogonal direction216. In several embodiments, first output reflector 220 may be amismatched impedance such as a prism, a right angle prism, or a mirror.In one embodiment, first output reflector 220 may have a coating thattransmits a pre-determined portion of electro-magnetic radiationspectrum. This might be used to discard unusable non-visible lightbefore it is coupled into an imager. In several embodiments,pre-determined portion of electromagnetic radiation spectrum may beinfrared light, visible light, a pre-determined band of wavelengths oflight, a specific color of light, or a combination thereof. In analternative embodiment, the coating may reflect infrared light, visiblelight, a pre-determined band of wavelengths of light, a specific colorof light, or some combination thereof.

In one embodiment, shown in FIG. 3A, a second output reflector 222 maybe disposed reflectably to second orthogonal direction 216. Secondoutput reflector 222 may reflect useful polarization light 204 in outputdirection 206. In another embodiment, shown in FIG. 4B, second outputreflector 222 may be disposed reflectably to output direction 206.Second output reflector 222 may reflect non-useful polarization light208 in second orthogonal direction 216. In several embodiments, secondoutput reflector 222 may be a mismatched impedance such as a prism, aright angle prism, or a mirror. In one embodiment, second outputreflector 222 may have a coating that transmits a pre-determined portionof electromagnetic radiation spectrum. This might be used to discardunusable non-visible light before it is coupled into an imager. Inseveral embodiments, pre-determined portion of electromagnetic radiationspectrum may be infrared light, visible light, a pre-determined band ofwavelengths of light, a specific color of light, or a combinationthereof. In an alternative embodiment, the coating may reflect infraredlight, visible light, a pre-determined band of wavelengths of light, aspecific color of light, or some combination thereof.

In one embodiment, initial reflector 214 may be disposed reflectably tofirst orthogonal direction 210. Initial reflector 214 may reflectnon-useful polarization light 208 in a second orthogonal direction 216substantially orthogonal to output direction 206 and first orthogonaldirection 210. In several embodiments, initial reflector 214 may be amismatched impedance such as a prism, a right angle prism, or a mirror.A mismatched impedance may reflect a wave, such as an electromagneticwave, in the manner of an echo. A mismatched impedance, for example, mayreflect part of a wave, or a range of wavelengths, while passing otherparts of the wave, or other wavelengths.

In one embodiment, initial reflector 214 may have a coating thattransmits a pre-determined portion of electromagnetic radiationspectrum. This might be used to discard unusable non-visible lightbefore it is coupled into an imager. In several embodiments,pre-determined portion of electromagnetic radiation spectrum may beinfrared light, visible light, a pre-determined band of wavelengths oflight, a specific color of light, or a combination thereof. In analternative embodiment, the coating may reflect infrared light, visiblelight, a pre-determined band of wavelengths of light, a specific colorof light, or some combination thereof.

In one embodiment, final reflector 218 may be disposed reflectably tosecond orthogonal direction 216. Final reflector 218 may reflectnon-useful polarization light 208 in output direction 206. In severalembodiments, final reflector 218 may be a mismatched impedance such as aprism, a right angle prism, or a mirror. In one embodiment, finalreflector 218 may have a coating that transmits a pre-determined portionof electromagnetic radiation spectrum. This might be used to discardunusable non-visible light before it is coupled into an imager. Inseveral embodiments, pre-determined portion of electromagnetic radiationspectrum may be infrared light, visible light, a pre-determined band ofwavelengths of light, a specific color of light, or a combinationthereof. In an alternative embodiment, the coating may reflect infraredlight, visible light, a pre-determined band of wavelengths of light, aspecific color of light, or some combination thereof.

In one embodiment, polarization 272 of non-useful polarization light 208may be rotated substantially to match polarization 270 of light ofuseful polarization 204 by initial and final reflectors 214 and 218. Inthis embodiment, first orthogonal direction 206 and second orthogonaldirection 216 may lie substantially in a plane of polarization 272 oflight of non-useful polarization 208. This basic block may be used toreflect and redirect light of non-useful polarization 208 frompolarizing beam splitter 202 as described above such that polarization272 of light of non-useful polarization 208 is converted to polarization270 of light of useful polarization 204 and redirected to outputdirection 206.

In an alternative embodiment, shown in FIG. 9, initial reflector 214 mayreflect light of non-useful polarization 208 about an axis in the planeof polarization 272 while final reflector 218 reflects light ofnon-useful polarization 208 about an axis substantially orthogonal toplane of polarization 272, thereby also causing light of non-usefulpolarization 208 to assume polarization 270. The light from finalreflector 218 may pass through a spacer 246 so that now-horizontallypolarized light of non-useful polarization 208 may exit at the sameplane as light of useful polarization 204. The two outputs may becoupled into output light pipe 232 to be homogenized and to have theirshape and NA converted to the shape and numerical aperture desired atthe output face. In one embodiment, output light pipe 232 may also usetotal internal reflection to propagate light to its output.

In one embodiment, light of useful polarization 204 may exit polarizingbeam splitter 202 in a different direction than that of light ofnon-useful polarization 208 after it has been redirected to outputdirection 206 by final reflector 218. In one embodiment, shown in FIG.3A, first output reflector 220 and second output reflector 222 may beused to redirect light of useful polarization 204 in the same directionas light of non-useful polarization 208. In an alternative embodiment,first output reflector 220, shown in FIG. 4A, redirects light of usefulpolarization 204 while second output reflector 222, shown in FIG. 4B,redirects light of non-useful polarization 208 in the same direction aslight of useful polarization 204. A spacer 246 may be used in eithercase to allow light of useful polarization 204 to exit at the samesurface as light of non-useful polarization 208. This may be useful inorder to couple light of useful polarization 204 and light of non-usefulpolarization 208 into output light pipe 232.

In one embodiment, supercube 268 may consist of polarizing beam splitter202 and reflectors 214, 218, 220 and 222. Light may be propagatedthrough these optical components via total internal reflection. Thesurfaces of the optical components may be optically polished to promotetotal internal reflection. In one embodiment the optical material usedfor reflectors 214, 218, 220 and 222 may have a high index of refractionto promote total internal reflection of skew rays. In one embodiment,the input and output faces of the optical components may be coated withan anti-reflective (AR) coating to minimize Fresnel reflection losses.

In one embodiment, reflectors 214, 218, 220 and 222 may be produced froman optical glass such as SF11 (n=1.785). In another embodiment,reflectors 214, 218, 220 and 222 may be produced from an optical glasssuch as BK7 (n=1.517). In this embodiment, however, the rays may startto leak out from the walls, particularly on the diagonal walls ofreflectors 214, 218, 220 and 222.

In one embodiment, a spacer 246 may be used in conjunction withreflectors 214, 218, 220 and 222 to form a large cubic shape for ease ofpackaging. In one embodiment, spacer 246 may be a cube. In oneembodiment, each of reflectors 214, 218, 220 and 222 may be combinedwith a complementary spacer 246, such as a right angle spacer, to form alittle cube. In one embodiment, eight little cubes may form a supercube268. In one embodiment, reflectors 214, 218, 220 and 222 and spacers 272are stacked together to form supercube 268. In one embodiment, thecomponents may be glued together by an adhesive material. In anotherembodiment, the components may be held together by means of a mechanicalholder. This construction may be rugged and may have minimal loss.

In several embodiments, gaps may be introduced between any two of inputand output light pipes 224 and 232, reflectors 244, 218, 220 and 222, orpolarizing beam splitter 202 to promote total internal reflection and toreduce losses. In one embodiment, input light pipe 224, reflectors 214,228, 220 and 222, and output light pipe 232 may be separated by smallair gaps.

In one embodiment, shown in FIG. 5, supercube 268 may be made up ofindividual components. In one embodiment, some of the components may becombined into single unit. In one embodiment, for example, two prismsmay be combined into a single prism. In this embodiment, a pair ofreflectors 214, 218, 220 or 222 may be combined during the manufacturingprocess, such as during a glass molding process. In an alternativeembodiment, two prisms may be glued together to form a single unit. Inone embodiment, two prisms may be combined with half of polarizing beamsplitter 202 to form a single unit. In this embodiment, the full PCSsystem may be made with two components together with the spacer 246. Inanother embodiment, a prism may be combined with a spacer 246. In oneembodiment, the system may be made in two components with the separationat polarizing beam splitter 202. In this embodiment, cost may beminimized.

In one embodiment, polarizing beam splitter 202 and reflectors 214, 218,220 and 222 may be substantially cubical. In one embodiment, polarizingbeam splitter 202 and reflectors 214, 218, 220 and 222 may have allsides with the substantially similar dimensions, except for thehypotenuses of the reflectors. In this embodiment, the output of inputlight pipe 224 may be square, and the input of output light pipe 232 maybe rectangular with an aspect ratio of 2:1. Non-cube configurations mayalso be implemented such that output light pipe 232 input has an aspectratio other than 2:1, albeit with possibly larger coupling losses.

In several embodiments, input and output light pipes 224 and 232,reflectors 214, 218, 220 and 222, or polarizing beam splitter 202 may becoated with an anti-reflection (AR) coating in order to increaseefficiency. In several embodiments, input and output light pipes 224 and232 may be tapered in an increasing or decreasing manner as required bythe application. Reflectors 214, 218, 220 and 222 may be reflectioncoated as appropriate for high angle light. Supercube 268 may be used invarious configuration besides the one described.

In one embodiment, an input light pipe 224 may be placed proximate to aninput 226 of polarizing beam splitter 202. In one embodiment, inputlight pipe 224 may have an input surface 228 and an output surface 230.In several embodiments, input light pipe 224 may be made of quartz,glass, plastic, or acrylic. In several embodiments, input light pipe 224may be a tapered light pipe (TLP) or a straight light pipe (SLP). Inseveral embodiments, a shape of input surface 228 may be flat, convex,concave, toroidal, or spherical, as shown in FIGS. 10A-10C. A surface ofinput light pipe 224 may be coated such that the total internalreflection preserves the polarization. The dimensions of input surface228 and output surface 230 may be selected such that the outputnumerical aperture (NA) is matched to a device receiving light frominput light pipe 224.

In one embodiment, output surface 230 may be disposed proximate to input226 of polarizing beam splitter 202. In several embodiments, a shape ofoutput surface 230 may be flat, convex, concave, toroidal, or spherical,as shown in FIGS. 10A-10C. In one embodiment, input light pipe 224 mayreceive substantially un-polarized light at input surface 228 andtransmit un-polarized light at output surface 230 to polarizing beamsplitter 202.

In one embodiment, input light pipe 224 may be hollow. Output surface230 may be a plano-convex lens. A convex surface of output surface 230may be spherical or cylindrical depending on the final configuration andcost of the components. A power of output surface 230 may be designedsuch that the light from output surface 230 is imaged onto polarizingbeam splitter 202. An inner surface of input light pipe 224 may becoated with a polarization preserving material.

In one embodiment, an output light pipe 232 may be placed proximate toan output 234 of supercube 268. In one embodiment, output light pipe 232may have an input surface 236 that is disposed proximate to outputdirection 206 and an output surface 238. Output light pipe 232 mayreceive useful polarization light 204 and non-useful polarization light208 at input surface 236 and may transmit useful polarization light 204and non-useful polarization light 208 at output surface 238.

In several embodiments, a shape of input surface 236 may be flat,convex, concave, toroidal, or spherical, as shown in FIGS. 10A-10C. Inseveral embodiments, a shape of output surface 238 may be flat, convex,concave, toroidal, or spherical, shown in FIGS. 10A-10C. In severalembodiments, output light pipe 232 may be comprised of a materialselected from group consisting of quartz, glass, plastic, or acrylic. Inseveral embodiments, output light pipe 232 may be a tapered light pipe(TLP) or a straight light pipe (SLP). A surface of output light pipe 232may be coated such that the total internal reflection preserves thepolarization. The dimensions of input surface 236 and output surface 238may be selected such that the output numerical aperture (NA) is matchedto a device receiving light from output light pipe 232.

In one embodiment, output light pipe 232 may be hollow. Output surface238 may be convex in shape. A convex surface of output surface 238 maybe spherical or cylindrical depending on the final configuration andcost of the components. A power of output surface 238 may be designedsuch that the light from output surface 238 is imaged onto an imageprojection system. An inner surface of output light pipe 232 may becoated with a polarization preserving material.

In one embodiment, a shell reflector 240 may reflect light from source212 to polarizing beam splitter 202. In one embodiment, shell reflector240 may have a coating that transmits a pre-determined portion ofelectromagnetic radiation spectrum. This might be used to discardunusable non-visible light before it is coupled into an imager. Inseveral embodiments, pre-determined portion of electromagnetic radiationspectrum may be infrared light, visible light, a pre-determined band ofwavelengths of light, a specific color of light, or a combinationthereof. In an alternative embodiment, the coating may reflect infraredlight, visible light, a pre-determined band of wavelengths of light, aspecific color of light, or some combination thereof.

In one embodiment, shell reflector 240 may have a first and a secondfocal points 242 and 244. In one embodiment, source 212 ofelectromagnetic radiation may be disposed substantially proximate tofirst focal point 242 of shell reflector 240 to emit rays of light thatreflect from shell reflector 240 and converge substantially at secondfocal point 244. In one embodiment, input surface 228 may be disposedproximate to second focal point 244 to collect and transmitsubstantially all of light. In another embodiment, input 226 ofpolarizing beam splitter 202 may be disposed proximate to second focalpoint 244 to collect and transmit substantially all of light. In severalembodiments, shell reflector 240 may be at least a portion of asubstantially elliptical surface of revolution, a substantiallyspherical surface of revolution, or a substantially toric surface ofrevolution.

In one embodiment, shell reflector 240 may include a primary reflector250 with a first optical axis 252, and first focal point 242 may be afocal point of primary reflector 250. In this embodiment, shellreflector 240 may also include a secondary reflector 254 having a secondoptical axis 256 placed substantially symmetrically to primary reflector250 such that first and second optical axes 252 and 256 aresubstantially collinear. In this embodiment, second focal point 244 maybe a focal point of secondary reflector 254, and rays of light mayreflect from primary reflector 250 toward secondary reflector 254 andconverge substantially at second focal point 244. In severalembodiments, primary and secondary reflectors 250 and 254 each may be asubstantially elliptical surface of revolution, or a substantiallyparabolic surface of revolution.

In one embodiment, primary reflector 250 may be at least a portion of asubstantially elliptical surface of revolution, and secondary reflector254 may be at least a portion of a substantially hyperbolic surface ofrevolution. In another embodiment, primary reflector 250 may be at leasta portion of a substantially hyperbolic surface of revolution, andsecondary reflector 254 may be at least a portion of a substantiallyelliptical surface of revolution.

Source 212 may be placed at first focal point 242 of primary reflector250 to collimate the collected light and direct it towards secondaryreflector 254. The output at input surface 228 may be directed into aninput light pipe 224. In one embodiment, input light pipe 224 may be atapered light pipe (TLP). Input light pipe 224 may be useful totransform a cross-sectional area or a numerical aperture of the image ofsource 212. The light may be directed into a supercube polarizationrecovery system to obtain linearly polarized light at output light pipe232. Linearly polarized light may be suitable for illumination ofLCD-based imager chips that require polarized light.

The degree of collimation may depend on the size of source 212.Secondary reflector 254 may be positioned symmetrically with respect toprimary reflector 250 such that they share common optical axes. The beamentering secondary reflector 254 converges to second focal point 244where a target, i.e., input light pipe 224, is placed. Input light pipe224 may couple light from second focal point 244 of secondary reflector254. In one embodiment, source 212 may be imaged onto a target in a 1:1ratio such that the brightness of source 212 is essentially preserved.The image of source 212 at input surface 228 may be exactly the same assource 212 with unit magnification, due to the 1:1 symmetry of thesystem.

Polarization recovery system 200 may be able to conserve etenduethroughout the source collector components of polarization recoverysystem 200. The full angle of light at input surface 228 may beapproximately 180° about an axis of source 212 and 90° about an axisnormal to the axis of source 212, due to the extent of the reflectors.These angles may be too large for applications such as micro displays.In one embodiment, input light pipe 224 may be a tapered light pipe(TLP) to transform a high input numerical aperture (NA) and small inputarea into a lower NA and larger output area without a loss ofbrightness, thus reducing the angles.

In one embodiment, source 212 may not be circular. In severalembodiments, the input of input light pipe 224 may be designed to be ofrectangular, elliptical, octagonal, or other cross-sectional shape tomatch the shape of the image of source 212. An input matched to theimage of source 212 may prevent or reduce degradation of system etenduedue to shape mismatches. The output dimensions and aspect ratios ofinput light pipe 224 may be designed to match a size and an aspect ratioof an imager panel, but with a super cube-based configuration they maybe relatively arbitrary.

Primary and secondary reflectors 250 and 254 may cover substantially arotational arc extent of 180° to maximize the collection efficiency,i.e., primary reflector 250 will collect approximately one half of thelight emitted from source 212. A retro-reflector 258 may be placed onthe opposite side of primary reflector 250 to collect the other half ofthe emitted light. In one embodiment, retro-reflector 258 may be ahemispherical retro-reflector. In one embodiment, a center of curvatureof retro-reflector 258 may be placed near source 212 of the lamp. Inthis embodiment, nearly all of the light may be reflected back throughsource 212 to be collected by primary reflector 250 and subsequentlyfocused into the light pipe. In practice, the efficiency ofretro-reflector 258 may be reduced as much as 60% to 80% by reflectivitylosses, Fresnel reflection losses, and distortion losses from theenvelope of source 212.

In one embodiment, a retro-reflector 258 may be disposed on a side ofsource 212 opposite shell reflector 240. In one embodiment,retro-reflector 258 may be a spherical retro-reflector. In oneembodiment, retro-reflector 258 may be integral to shell reflector 240.In one embodiment, retro-reflector 258 may have a coating that transmitsa pre-determined portion of electromagnetic radiation spectrum. Thismight be used to discard unusable non-visible light before it is coupledinto an imager. In several embodiments, pre-determined portion ofelectro-magnetic radiation spectrum may be infrared light, visiblelight, a pre-determined band of wavelengths of light, a specific colorof light, or a combination thereof. In an alternative embodiment, thecoating may reflect infrared light, visible light, a pre-determined bandof wavelengths of light, a specific color of light, or some combinationthereof.

In one embodiment of the invention an image projection system 260 may bedisposed proximate to output direction 206 to collect substantially allof useful polarization light 204. In several embodiments, imageprojection system 260 may be a liquid crystal on silicon (LCOS) imager,a digital micromirror device (DMD) chip, or a transmissive liquidcrystal display (LCD) panel.

In one embodiment of the invention a focusing lens 262 may be disposedproximate to output direction 206, with image projection system 260disposed proximate to an output side 264 of focusing lens 262. An image266 illuminated by useful polarization light 204 collected and focusedat focusing lens 262 will be released by the projection system 260 todisplay the image 266.

In one embodiment of the invention, a method of polarization recoverymay include the steps of polarizing substantially light into light ofuseful polarization 204 and light of non-useful polarization 208,transmitting useful polarization light 204 in an output direction 206,reflecting non-useful polarization light 208 in a first orthogonaldirection 210 substantially orthogonal to output direction 206,reflecting non-useful polarization light 208 in a second orthogonaldirection 216 substantially orthogonal to output direction 206 and firstorthogonal direction 210, and reflecting non-useful polarization light208 in output direction 206.

While the invention has been described in detail above, the invention isnot intended to be limited to the specific embodiments as described. Itis evident that those skilled in the art may now make numerous uses andmodifications of and departures from the specific embodiments describedherein without departing from the inventive concepts.

1. A polarization recovery apparatus comprising: a polarizing beamsplitter transmitting a light of a useful polarization in an outputdirection and reflecting a light of a non-useful polarization in a firstorthogonal direction substantially orthogonal to said output direction;an initial reflector disposed reflectably to said orthogonal direction,said initial reflector reflecting said non-useful polarization light ina second orthogonal direction substantially orthogonal to said outputdirection and said first orthogonal direction; and a final reflectordisposed reflectably to said second orthogonal direction, said finalreflector reflecting said non-useful polarization light in said outputdirection; wherein said non-useful polarization light is rotatedsubstantially to light of said useful polarization by said initial andfinal reflectors. 2-6. (canceled)
 7. The polarization recovery apparatusof claim 1, comprising further: an input light pipe having an inputsurface and an output surface, said output surface disposed proximate toan input face of said polarizing beam splitter, said input light pipereceiving substantially un-polarized light at said input surface andtransmitting said un-polarized light at said output surface to saidpolarizing beam splitter.
 8. The polarization recovery apparatus ofclaim 7, wherein a shape of said input surface is selected from thegroup consisting of: flat, convex, concave, toroidal, and spherical. 9.The polarization recovery apparatus of claim 7, wherein a shape of saidoutput surface is selected from the group consisting of: flat, convex,concave, toroidal, and spherical.
 10. The polarization recoveryapparatus of claim 7, wherein said input light pipe is comprised of amaterial selected from the group consisting of quartz, glass, plastic,or acrylic.
 11. The polarization recovery apparatus of claim 7, whereinsaid input light pipe is selected from the group consisting of: astraight light pipe (SLP), and a tapered light pipe (TLP). 12-16.(canceled)
 17. The polarization recovery apparatus of claim 1, whereinsaid initial reflector is selected from the group consisting of: aprism, a right angle prism, a mismatched impedance, and a mirror. 18.(canceled)
 19. The polarization recovery of claim 1, wherein said finalreflector is selected from the group consisting of: a prism, a rightangle prism, a mismatched impedance, and a mirror.
 20. (canceled) 21.The polarization recovery apparatus of claim 1, comprising further: ashell reflector having a first and a second focal points; a source ofelectromagnetic radiation disposed proximate to said first focal pointof said shell reflector to emit rays of light that reflect from saidshell reflector and converge substantially at said second focal point;wherein said input surface is disposed proximate to said second focalpoint to collect and transmit substantially all of said light.
 22. Thepolarization recovery apparatus of claim 21, wherein said shellreflector comprises at least a portion of a shape selected from thegroup consisting of: a substantially elliptical surface of revolution, asubstantially spherical surface of revolution, and a substantially toricsurface of revolution. 23-30. (canceled)
 31. The polarization recoveryapparatus of claim 21, wherein said source of electro-magnetic radiationcomprises an arc lamp.
 32. The polarization recovery apparatus of claim31, wherein said arc lamp comprises a lamp selected from the groupconsisting of a xenon lamp, a metal halide lamp, a UHP lamp, a HID lamp,or a mercury lamp.
 33. The polarization recovery apparatus of claim 21,wherein said source of electromagnetic radiation is selected from thegroup consisting of a halogen lamp, and a filament lamp.
 34. Thepolarization recovery apparatus of claim 1, comprising further: an imageprojection apparatus disposed proximate to said output direction tocollect substantially said useful polarization light.
 35. Thepolarization recovery apparatus of claim 34, wherein said imageprojection apparatus is selected from the group consisting of: an LCOSimager, a DMD chip, and a transmissive LCD panel.
 36. The polarizationrecovery apparatus of claim 21, wherein a shape of said polarizing beamsplitter is matched substantially to an aperture of said source ofelectro-magnetic radiation.
 37. The polarization recovery apparatus ofclaim 1, wherein said polarizing beam splitter comprises a wire-gridpolarizing beam splitter.
 38. A method of polarization recoverycomprising: polarizing substantially light into light of a usefulpolarization and light of a non-useful polarization; transmitting saiduseful polarization light in an output direction; reflecting saidnon-useful polarization light in a first orthogonal directionsubstantially orthogonal to said output direction; reflecting saidnon-useful polarization light in a second orthogonal directionsubstantially orthogonal to said output direction and said firstorthogonal direction; and reflecting said non-useful polarization lightin said output direction.
 39. A system of polarization recoverycomprising: means for polarizing substantially light into light of auseful polarization and light of a non-useful polarization; means fortransmitting said useful light in an output direction; means forreflecting said non-useful light in a first orthogonal directionsubstantially orthogonal to said output direction; means for reflectingsaid non-useful light in a second orthogonal direction substantiallyorthogonal to said output direction and said first orthogonal direction;and means for reflecting said non-useful light in said output direction.